Not since the Reese's Peanut Butter Cups have there been two great populist tastes that go so great together. In an amazing bit of fact-free scare mongering gauged to panic everyone across the political spectrum, Michael Oppenheimer (embarrassingly a professor at my alma mater) manages to combine demagoguing against Mexican immigration with climate alarmism

Now, scientists are predicting another consequence of climate change: mass migration to the United States.

Between 1.4 million and 6.7 million Mexicans could migrate to the U.S. by 2080 as climate change reduces crop yields and agricultural production in Mexico, according to a study published online this week in the Proceedings of the National Academy of Sciences. The number could amount to 10% of the current population of Mexicans ages 15 to 65.

The proceedings of the NAS has become a joke of late. Roger Pielke Jr responded:

To be blunt, the paper is guesswork piled on top of "what ifs" built on a foundation of tenuous assumptions. The authors seem to want to have things both ways -- they readily acknowledge the many and important limitations of their study, but then go on to assert that "it is nevertheless instructive to predict future migrant flows for Mexico using the estimates at hand to assess the possible magnitude of climate change"“related emigration." It can't be both -- if the paper has many important limitations, then this means that that it is not particularly instructive. With respect to predicting immigration in 2080 (!), admitting limitations is no serious flaw.

To use this paper as a prediction of anything would be a mistake. It is a tentative sensitivity study of the effects of one variable on another, where the relationship between the two is itself questionable but more importantly, dependent upon many other far more important factors. The authors admit this when they write, "It is important to note that our projections should be interpreted in a ceteris paribus manner, as many other factors besides climate could potentially influence migration from Mexico to the United States." but then right after they assert, "Our projections are informative,nevertheless, in quantifying the potential magnitude of impacts of climate change on out-migration." It is almost as if the paper is written to be misinterpreted

I thought this response was instructive

Philip Martin, an expert in agricultural economics at UC Davis, said that he hadn't read the study but that making estimates based solely on climate change was virtually impossible.

"It is just awfully hard to separate climate change from the many, many other factors that affect people's decisions whether to stay in agriculture or move," he said.

The same exact statement, by the way, could be made as to the relationship of climate change to the single variable manmade CO2 without reference to the myriad of other factors that affect the complex climate system.